Homodimerization of adenosine A₁ receptors in brain cortex explains the biphasic effects of caffeine

Eduard Gracia; Estefania Moreno; Antoni Cortés; Carme Lluís; Josefa Mallol; Peter J McCormick; Enric I Canela; Vicent Casadó

doi:10.1016/j.neuropharm.2013.03.005

Homodimerization of adenosine A₁ receptors in brain cortex explains the biphasic effects of caffeine

Neuropharmacology. 2013 Aug:71:56-69. doi: 10.1016/j.neuropharm.2013.03.005. Epub 2013 Mar 22.

Authors

Eduard Gracia¹, Estefania Moreno, Antoni Cortés, Carme Lluís, Josefa Mallol, Peter J McCormick, Enric I Canela, Vicent Casadó

Affiliation

¹ Centro de Investigación Biomédica en Red sobre Enfermedades Neurodegenerativas (CIBERNED), Faculty of Biology, University of Barcelona, Av. Diagonal 643, 08028 Barcelona, Spain. edugss@gmail.com

PMID: 23523559
DOI: 10.1016/j.neuropharm.2013.03.005

Abstract

Using bioluminescence resonance energy transfer and proximity ligation assays, we obtained the first direct evidence that adenosine A₁ receptors (A₁Rs) form homomers not only in cell cultures but also in brain cortex. By radioligand binding experiments in the absence or in the presence of the A₁Rs allosteric modulator, adenosine deaminase, and by using the two-state dimer receptor model to fit binding data, we demonstrated that the protomer-protomer interactions in the A₁R homomers account for some of the pharmacological characteristics of agonist and antagonist binding to A₁Rs. These pharmacological properties include the appearance of cooperativity in agonist binding, the change from a biphasic saturation curve to a monophasic curve in self-competition experiments and the molecular cross-talk detected when two different specific molecules bind to the receptor. In this last case, we discovered that caffeine binding to one protomer increases the agonist affinity for the other protomer in the A₁R homomer, a pharmacological characteristic that correlates with the low caffeine concentrations-induced activation of agonist-promoted A₁R signaling. This pharmacological property can explain the biphasic effects reported at low and high concentration of caffeine on locomotor activity.

Publication types

Research Support, Non-U.S. Gov't

MeSH terms

Adenosine A1 Receptor Agonists / chemistry
Adenosine A1 Receptor Agonists / metabolism
Adenosine A1 Receptor Agonists / pharmacology*
Adenosine A1 Receptor Antagonists / chemistry
Adenosine A1 Receptor Antagonists / metabolism
Adenosine A1 Receptor Antagonists / pharmacology*
Adenosine Deaminase / chemistry
Adenosine Deaminase / metabolism
Allosteric Site / drug effects
Animals
Bacterial Proteins / genetics
Bacterial Proteins / metabolism
Caffeine / chemistry
Caffeine / metabolism
Caffeine / pharmacology*
Cattle
Cell Membrane / drug effects
Cell Membrane / metabolism
Central Nervous System Stimulants / chemistry
Central Nervous System Stimulants / metabolism
Central Nervous System Stimulants / pharmacology
Cerebral Cortex / cytology
Cerebral Cortex / drug effects*
Cerebral Cortex / metabolism
Dimerization
HEK293 Cells
Humans
Kinetics
Luminescent Proteins / genetics
Luminescent Proteins / metabolism
Models, Biological
Nerve Tissue Proteins / agonists
Nerve Tissue Proteins / antagonists & inhibitors
Nerve Tissue Proteins / chemistry
Nerve Tissue Proteins / metabolism*
Neurons / cytology
Neurons / drug effects*
Neurons / metabolism
Receptor, Adenosine A1 / chemistry
Receptor, Adenosine A1 / genetics
Receptor, Adenosine A1 / metabolism*
Recombinant Fusion Proteins / metabolism

Substances

Adenosine A1 Receptor Agonists
Adenosine A1 Receptor Antagonists
Bacterial Proteins
Central Nervous System Stimulants
Luminescent Proteins
Nerve Tissue Proteins
Receptor, Adenosine A1
Recombinant Fusion Proteins
yellow fluorescent protein, Bacteria
Caffeine
Adenosine Deaminase